Abstract. The transition, in extent and characteristics, of
atmospheric emissions caused by the modernization of the heavy-duty on-road
fleet was studied utilizing roadside measurements. Emissions of particle
number (PN), particle mass (PM), black carbon (BC), nitrogen oxides
(NOx), carbon monoxide (CO), hydrocarbon (HC), particle size
distributions, and particle volatility were measured from 556 individual
heavy-duty trucks (HDTs). Substantial reductions in PM, BC, NOx, CO, and
to a lesser extent PN were observed from Euro III to Euro VI HDTs by 99 %,
98 %, 93 %, and 57 % for the average emission factors of PM, BC,
NOx, and CO, respectively. Despite significant total reductions in
NOx emissions, the fraction of NO2 in the NOx emissions
increased continuously from Euro IV to Euro VI HDTs. Larger data scattering
was evident for PN emissions in comparison to solid particle number (SPN)
for Euro VI HDTs, indicating a highly variable fraction of volatile particle
components. Particle size distributions of Euro III to enhanced environmentally friendly vehicle (EEV) HDTs were
bimodal, whereas those of Euro VI HDTs were nucleation mode dominated. High
emitters disproportionately contributed to a large fraction of the total
emissions with the highest-emitting 10 % of HDTs in each pollutant
category being responsible for 65 % of total PM, 70 % of total PN, and
44 % of total NOx emissions. Euro VI HDTs, which
accounted for 53 % of total kilometres driven by Swedish HDTs, were
estimated to only contribute to 2 %, 6 %, 12 %, and 47 % of PM, BC,
NOx, and PN emissions, respectively. A shift to a fleet dominated by Euro VI HDTs would
promote a transition of atmospheric emissions towards low PM, BC, NOx,
and CO levels. Nonetheless, reducing PN, SPN, and NO2 emissions from
Euro VI HDTs is still important to improve air quality in urban
environments.